Krystof Zizka, a co-owner of the restaurant, says he doesn’t make a penny on the oysters, though they are one of the reasons his three-year-old restaurant is so successful. ¶ The cheap late-afternoon oyster is to a restaurant what a liter bottle of Coca-Cola is to a supermarket: the loss leader that gets customers in the door, at which point they buy something else at full price.